In the medical field, implantable leads are used with a wide variety of medical devices. For example, implantable leads are commonly used to form part of implantable cardiac pacemakers that provide therapeutic stimulation to the heart by delivering pacing, cardioversion or defibrillation pulses. The pulses can be delivered to the heart via electrodes disposed on the leads, e.g., typically near distal ends of the leads. In that case, the leads may be used to position the electrodes with respect to various cardiac locations so that the pacemaker can deliver pulses to the appropriate locations. Leads are also used for sensing purposes, or for both sensing and stimulation purposes. Implantable leads are also used in neurological devices, muscular stimulation therapy, and devices that sense chemical conditions in a patient's blood or gastric system stimulators.
Another type of IMD is an implantable neurological stimulation device (sometimes referred to as an implantable neurostimulator or INS). INS devices can generate electrical stimulation signals that are used to influence the human nervous system or organs. Conventionally, the INS devices have been surgically implanted into a patient in a subcutaneous pocket in the abdomen, pectoral region, or upper buttocks area. Electrical contacts carried on the distal end of a lead are placed at the desired stimulation site (e.g., at a location in the spine or directly in the brain) and the proximal end of the lead is connected to the INS. The lead typically has one or more insulated electrical conductors (filers) that connect the electrical contacts, or electrodes, to the INS. For neurostimulation of the spine or brain, the leads may typically have 4 or 8 sets of conductors and electrodes.
It may be desirable to implant the INS at a location in the patient's head in cases where the distal end of the lead is provided at a site directly in the brain. For example, it may be desirable to implant the INS under the scalp on top of the patient's head (either on top of the surface of the skull or in a pocket formed in the skull).
Deep brain stimulation implants may be used for the treatment of a variety of diseases including epilepsy and Parkinson's Disease. In these devices, the electrodes are implanted in the brain of the patient to provide electric stimulation to affected regions of the brain.
Alternatively, the leads may be placed in the epidural region of the spine to stimulate the dorsal horn of the spinal cord for the treatment of pain, or other diseases such as angina.
Occasionally, patients that have implantable leads may benefit from a magnet resonance image (MRI) being taken of a particular area of his or her body, such as to monitor a disease or to diagnose an unrelated injury or disorder. MRI systems use radio frequency radiation in the presence of a strong magnetic field to produce diagnostic images of the patient. MRI techniques can achieve an effective image of the soft tissues of the heart and vascular system. MRI procedures can also image these features without delivering a high dosage of radiation to the body of the patient, and as a result, MRI procedures may be repeated reliably and safely. However, MRI devices may operate at frequencies of 10 megahertz or higher, which may cause energy to be transferred to the lead and can produce a voltage that can interact with surrounding tissue.